1. Technical Field
The present invention relates to a via formation system and more particularly to a laser system used for forming a micro via.
2. Related Art
FIGS. 1-5 illustrate a related art method of forming a microvia over a plated through hole (PTH) of a substrate. In particular, FIG. 1 illustrates a cross sectional view of a related art substrate 12, having a PTH 10 formed therein. The PTH 10 includes an opening 14 and a capture pad 16 formed using conventional techniques. As illustrated in FIG. 2, a dielectric material 18 is deposited within the opening 14 of the PTH 10, filling the opening 14 of the PTH 10, and coating a lower surface 20 of the substrate 12. A plated stud 22 is attached to a capture pad 24 of the PTH 10, as shown in FIG. 3. FIG. 4 illustrates an additional step after related art FIG. 3 wherein a dielectric material 18B is added to a top surface 26 of the substrate 12. A cavity 16 is formed in the dielectric material 18B by chemical etching, drilling or other mechanical method. The plated stud 22 is required to protect the dielectric material 18B from being removed by the chemical etching or drilling processes used during formation of the cavity 16. FIG. 5 illustrates related art FIG. 4 after an object 28, such as a microvia, is attached to the plated stud 22.
A first general aspect of the present invention provides a laser beam system comprising:
a laser system providing a bimodal focused beam, and wherein an energy density at a centroid of the beam is at least 10 percent less than the average energy density of the beam.
A second general aspect of this invention provides an apparatus comprising:
a laser source producing a laser beam; and
a beam shaping lens for forming the laser beam into a bimodal focused beam wherein an area of reduced energy density at a centroid of the bimodal focused beam is at least 10% less than an average energy density of the bimodal focused beam.
A third general aspect of this invention provides a method comprising:
applying a focused laser beam onto a circuit board wherein the focused laser beam removes a dielectric above a surface of a capture pad of a Plated Through Hole (PTH) while maintaining the dielectric within the PTH to a substantially flush level with the surface of the capture pad.